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Abstract:

Disclosed is a structure for raising the Q-value of a near-field antenna
used by a non-contact power transmission device that utilizes magnetic
field coupling in the near field in a manner improving the efficiency of
power transmission. The near-field antenna used by the non-contact power
transmission device galvanically isolates a resonant circuit including a
resonant first inductor 31 and a first capacitor 32 from a transmission
circuit or a reception circuit and, through electromagnetic coupling or
inductive coupling established between the transmission or reception
circuit and the near-field antenna using a second inductor 33 or a second
capacitor 34, maintains a high Q even if the coupling between the
antennas weakens due to an extended distance the antennas.

Claims:

1. A non-contact power transmission device using magnetic field coupling
in a near field, comprising: a transmission-side apparatus including at
least a high-frequency AC power source and a near-field antenna and
transmitting high-frequency power; and a reception-side apparatus
including at least a load and a near-field antenna and receiving the
high-frequency power transmitted from the transmission-side apparatus,
wherein the near-field antenna included in the transmission-side
apparatus or in the reception-side apparatus includes: a first inductor
for resonance; a first capacitor connected with the first inductor to
adjust an oscillating frequency; and a coupling means formed in a manner
faradically isolated from a resonant circuit including the first inductor
and the first capacitor, the coupling means supplying AC power from the
high-frequency AC power source of the transmission-side apparatus to the
resonant circuit including the first inductor and the first capacitor,
the coupling means further supplying alternatively the high-frequency
power received by the resonant circuit including the first inductor and
the first capacitor to the load of the reception-side apparatus.

2. The non-contact power transmission device according to claim 1,
wherein the coupling means is constituted by a second inductor coupled
electromagnetically with the first inductor for resonance.

3. The non-contact power transmission device according to claim 2,
wherein the second inductor constituting the coupling means is formed
with electrodes made of thin metallic films over the same dielectric
substrate along with the first inductor constituting the resonant circuit
and the first capacitor for adjusting the oscillating frequency.

4. The non-contact power transmission device according to claim 3,
wherein the second inductor constituting the coupling means is formed
outside the first inductor and the first capacitor is positioned inside
the first inductor over the same dielectric substrate.

5. The non-contact power transmission device according to claim 3,
wherein the second inductor constituting the coupling means is formed
inside the first inductor and the first capacitor is positioned outside
the inductor over the same dielectric substrate.

6. The non-contact power transmission device according to claim 1,
wherein the coupling means is constituted by a second capacitor coupled
electromagnetically with the first inductor for resonance.

7. The non-contact power transmission device according to claim 6,
wherein the second capacitor constituting the coupling means is formed on
one side of the same dielectric substrate and the first capacitor is
formed on the other side of the same dielectric substrate, the second
capacitor and the first capacitor being positioned in close proximity to
each other.

8. The non-contact power transmission device according to claim 7,
wherein electrodes positioned on both sides of the same dielectric
substrate in close proximity to one another are partially made of
comb-tooth electrodes to form the first capacitor and the second
capacitor constituting the coupling means.

9. A near-field antenna included in a transmission-side apparatus or a
reception-side apparatus of a non-contact power transmission device using
magnetic field coupling in a near field, the near-field antenna
comprising: a first inductor for resonance; a first capacitor connected
with the first inductor to adjust an oscillating frequency; and a
coupling means isolated faradically from a resonant circuit including the
first inductor and the first capacitor, the coupling means supplying AC
power from the outside to the resonant circuit including the first
inductor and the first capacitor, the coupling means further supplying
alternatively received high-frequency power to the outside.

10. The near-field antenna according to claim 9, wherein the coupling
means is constituted by a second inductor coupled electromagnetically
with the first inductor for resonance.

11. The near-field antenna according to claim 10, wherein the second
inductor constituting the coupling means is formed with electrodes made
of thin metallic films over the same dielectric substrate along with the
first inductor constituting the resonant circuit and the first capacitor
for adjusting the oscillating frequency.

12. The near-field antenna according to claim 11, wherein the second
inductor constituting the coupling means is formed outside the first
inductor and the first capacitor is positioned inside the first inductor
over the same dielectric substrate.

13. The near-field antenna according to claim 11, wherein the second
inductor constituting the coupling means is formed inside the first
inductor and the first capacitor is positioned outside the inductor over
the same dielectric substrate.

14. The near-field antenna according to claim 9, wherein the coupling
means is constituted by a second capacitor coupled electromagnetically
with the first inductor for resonance.

15. The near-field antenna according to claim 14, wherein the second
capacitor constituting the coupling means is formed on one side of the
same dielectric substrate and the first capacitor is formed on the other
side of the same dielectric substrate, the second capacitor and the first
capacitor being positioned in close proximity to each other.

16. The near-field antenna according to claim 15, wherein electrodes
positioned on both sides of the same dielectric substrate in close
proximity to one another are partially made of comb-tooth electrodes to
form the first capacitor and the second capacitor constituting the
coupling means.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a non-contact power transmission
device that supplies power to various types of electronic equipment in
non-contact system. More particularly, the invention relates to a
non-contact power transmission device capable of enhancing the efficiency
of power transmission in a non-contact manner through magnetic field
coupling in the near field and to a novel near-field antenna for use with
that non-contact power transmission device.

BACKGROUND ART

[0002] The devices and schemes for transmitting and receiving power in
non-contact system utilize extensively a so-called electromagnetic
induction method involving the use of interactions between inductors.
Typical applications making use of this electromagnetic induction method,
all well-known and already commercialized, include non-contact recharging
of electric toothbrushes, electric shavers and portable digital devices;
non-contact supply of power to IC cards exemplified by SUICA offered by
East Japan Railway Company; and wireless recharging equipment for
electric vehicles.

[0003] These non-contact power transmission devices generally have the
primary coil installed on the side of non-contact power transmission and
the secondary coil on the side of non-contact power reception. By
applying high-frequency AC power generated within the non-contact power
transmission side, the non-contact power transmission device allows a
high-frequency magnetic field to be generated on the primary coil or an
inductor on the transmission side, thereby causing an induced current to
be generated on the secondary coil or an inductor on the reception side.
The non-contact power transmission device then accomplishes wireless
power transmission by converting high-frequency power induced on the
secondary coil into a DC current and supplying the induced DC current to
the load on the reception side. A basic configuration of such a
non-contact power transmission device has been disclosed in Patent
Literature 1 cited below.

[0004] Because the above-described non-contact power transmission device
permits power transmission through magnetic field coupling in the near
field between the transmission-side inductor and the reception-side
inductor, these inductors are also called a near-field antenna each. FIG.
12 accompanying this description shows a basic configuration of a
prior-art non-contact power transmission device.

[0005] As can be seen from FIG. 12, the transmission side of the
non-contact power transmission device is configured to be furnished with
an AC power source that generates a high frequency, a control circuit
that turns on and off the transmission output, and a matching circuit
that matches the impedance of an antenna with that of other circuits.
This matching circuit is configured to be connected with a near-field
antenna for transmitting power. The reception side in FIG. 12 is
configured to be furnished with a load that acts as a functional device,
a rectification circuit that converts AC power into a DC current, a
near-field antenna, and a matching circuit that matches the impedance of
an antenna with that of other circuits. This matching circuit is also
configured to be connected with a near-field antenna for receiving power.

[0006] FIG. 13 accompanying this description shows a detailed
configuration of the near-field antennas of the above-described
non-contact power transmission device. Specifically, the
transmission-side antenna and reception-side antenna have basically the
same shape; they are each shaped to be a coil that generates a magnetic
field. The transmission-side coil or inductor is directly connected with
a transmission circuit comprised of an AC power source, an ON/OFF control
circuit, and an impedance matching circuit. Likewise, the reception-side
coil or inductor is directly connected with a reception circuit comprised
of a load, a rectification circuit, and an impedance matching circuit.

[0007] As explained, the non-contact power transmission device disclosed
in the above-cited Patent Literature 1 utilizes magnetic field coupling
in the near field. The degree of coupling between the inductor of the
near-field antenna on the transmission side and the inductor of the
near-field antenna on the reception side is given by the coupling
coefficient K of the mathematical expression shown below. In this
expression, M12 denotes the mutual inductance between the
transmission-side inductor and the reception-side inductor, and L1
and L2 represent the self-inductance of each of the inductors.

K = M 12 L 1 L 2 [ Math . 1 ]
##EQU00001##

[0008] As can be seen from the above mathematical expression, the
above-mentioned coupling coefficient K is a function of the geometric
shapes of the inductors and the distance between the inductors. As the
distance between the inductors increases, the coupling coefficient K
drops abruptly in inverse proportion to the inductor-to-inductor distance
raised to the third power. Thus the prior-art non-contact power
transmission device described above has this problem: as the distance
between the transmission-side near-field antenna and the reception-side
near-field antenna increases, the degree of coupling between the antennas
decreases, thereby limiting the distance of non-contact power
transmission and reception.

[0009] As a countermeasure to the above problem, Non Patent Literature 1
cited below introduces a method for raising the degree of coupling
between the transmission-side inductor and the reception-side inductor,
both near-field antennas, by optimizing their shapes. Non Patent
Literature 1 further discloses a method for extending the distance of
power transmission of which the efficiency is improved by the above
method.

[0012] However, the methods disclosed in the above-cited Patent Literature
1 and Non Patent Literature 1 still leave the original coupling
coefficient dropping in inverse proportion to the coil-to-coil distance
raised to the third power, even when the degree of coupling between the
transmission-side inductor and the reception-side inductor is elevated.
Thus the problem remains that as the distance between the inductors is
extended, the efficiency of power transmission abruptly drops, limiting
the distance over which power can be transmitted and received in
non-contact system.

[0013] It is therefore an object of the present invention to overcome the
above problem of the prior art and to provide a technique for improving
the efficiency of power transmission, as well as a non-contact power
transmission device configured to be capable of extending the distance of
non-contact power transmission.

Solution to Problem

[0014] In achieving the foregoing object of the present invention, there
is provided a non-contact power transmission device using magnetic field
coupling in a near field, the non-contact power transmission device
including a transmission-side apparatus including at least a
high-frequency AC power source and a near-field antenna and transmitting
high-frequency power, and a reception-side apparatus including at least a
load and a near-field antenna and receiving the high-frequency power
transmitted from the transmission-side apparatus. The near-field antenna
included in the transmission-side apparatus or in the reception-side
apparatus includes a first inductor for resonance, a first capacitor
connected with the first inductor to adjust an oscillating frequency, and
a coupling means formed in a manner faradically isolated from a resonant
circuit including the first inductor and the first capacitor, the
coupling means supplying AC power from the high-frequency AC power source
of the transmission-side apparatus to the resonant circuit including the
first inductor and the first capacitor, the coupling means further
supplying alternatively the high-frequency power received by the resonant
circuit including the first inductor and the first capacitor to the load
of the reception-side apparatus.

[0015] With the non-contact power transmission device according to the
present invention, the coupling means may preferably be constituted by a
second inductor coupled electromagnetically with the first inductor for
resonance. Also, the second inductor constituting the coupling means may
preferably be formed with electrodes made of thin metallic films over the
same dielectric substrate along with the first inductor constituting the
resonant circuit and the first capacitor for adjusting the oscillating
frequency. Further, the second inductor constituting the coupling means
may preferably be formed outside the first inductor and the first
capacitor may preferably be positioned inside the first inductor over the
same dielectric substrate. Alternatively, the second inductor
constituting the coupling means may preferably be formed inside the first
inductor and the first capacitor may preferably be positioned outside the
inductor over the same dielectric substrate.

[0016] Furthermore, in achieving also the foregoing object of the present
invention, the above-outlined non-contact power transmission device may
preferably have the coupling means constituted by a second capacitor
coupled electromagnetically with the first inductor for resonance.
Moreover, the second capacitor constituting the coupling means may
preferably be formed on one side of the same dielectric substrate and the
first capacitor may preferably be formed on the other side of the same
dielectric substrate, the second capacitor and the first capacitor being
positioned in close proximity to each other. And electrodes positioned on
both sides of the same dielectric substrate in close proximity to one
another may preferably be partially made of comb-tooth electrodes to form
the first capacitor and the second capacitor constituting the coupling
means.

Advantageous Effects of Invention

[0017] As described above, according to the non-contact power transmission
device or the near-field antenna thereof of the present invention,
separating the transmission and reception circuits from the near-field
antennas contributes to raising the Q-value of the antennas. As a result,
even if the distance between the two antennas is extended and the degree
of coupling between the resonance-use inductors of the transmitting and
receiving antennas is lowered thereby, it is possible to provide higher
efficiency of power transmission and a longer distance of power
transmission than prior-art non-contact power transmission systems.

BRIEF DESCRIPTION OF DRAWINGS

[0018] FIG. 1 is a block diagram showing a configuration of a non-contact
power transmission device using the magnetic field in the near field
according to the present invention.

[0019]FIG. 2 is a plan view showing a theoretical configuration of a
near-field antenna for the non-contact power transmission device as
example 1 of the present invention.

[0020]FIG. 3 is a perspective view showing a detailed configuration of
the near-field antenna as the example 1.

[0021]FIG. 4 is a circuit diagram showing a circuit configuration of a
non-contact power transmission device utilizing the near-field antenna as
the example 1.

[0022]FIG. 5 is a plan view showing a theoretical configuration of a
near-field antenna for the non-contact power transmission device as
example 2 of the present invention.

[0023] FIG. 6 is a perspective view showing a detailed configuration of
the near-field antenna as the example 2.

[0024]FIG. 7 is a plan view showing a theoretical configuration of a
near-field antenna for the non-contact power transmission device as
example 3 of the present invention.

[0025]FIG. 8 is a perspective view showing a detailed configuration of
the near-field antenna as the example 3.

[0026]FIG. 9 is a circuit diagram showing a circuit configuration of a
non-contact power transmission device utilizing the near-field antenna as
the example 3.

[0027]FIG. 10 is a graphic representation comparing the non-contact power
transmission device of the present invention with a prior-art non-contact
power transmission device in terms of power transmission efficiency.

[0028]FIG. 11 is a graphic representation showing changes in the ratio of
power transmission efficiency between the inventive non-contact power
transmission device and the prior-art non-contact power transmission
device with regard to normalized distances.

[0029]FIG. 12 is a plan view showing a configuration of a near-field
antenna for the prior-art non-contact power transmission device.

[0030] FIG. 13 is a circuit diagram showing a circuit configuration of a
non-contact power transmission device utilizing the above-mentioned
prior-art near-field antenna.

DESCRIPTION OF EMBODIMENTS

[0031] Some examples of the present invention will be described below in
detail by reference to the accompanying drawings.

[0032] FIG. 1 accompanying this description shows a configuration of a
non-contact power transmission device according to the present invention.
In FIG. 1, a transmission side 10 includes an AC power source 14 that
generates a high frequency, an ON/OFF control circuit 13 that turns on
and off transmission output, and an impedance matching circuit 12 that
matches the impedance of an antenna with that of the other circuits.
These components make up a so-called a transmission circuit 15. This
transmission circuit 15, particularly the output of its impedance
matching circuit 12, is connected to a near-field antenna 11 for
transmitting power.

[0033] On the other hand, the reception side in FIG. 1 includes a load 24
that acts as a functional device, a rectification circuit 23 that
converts AC power into DC power and supplies the DC power to the load 24,
and an impedance matching circuit 22 that matches the impedance of a
near-field antenna with that of the other circuits. These components make
up a so-called reception circuit 25. This reception circuit 25,
particularly the input of its impedance matching circuit 22, is connected
to a near-field antenna 21 for receiving power.

[0034] Below is a description of a near-field antenna used by the
non-contact power transmission device of the present invention, in
comparison to the near-field antenna used by a common non-contact power
transmission system.

<Near-Field Antennas for the Prior-Art Non-Contact Power Transmission
System>

[0035] A common non-contact power transmission system usually has a
capacitor connected to each of a transmission-side inductor and a
reception-side inductor, and causes these capacitors to operate at a
resonant frequency in order to maximize the efficiency of power
transmission. In this configuration, the capacitors play the role of
synchronizing the frequency of the transmission-side inductor with that
of the reception-side inductor.

[0036]FIG. 12 accompanying this description shows a typical configuration
of a near-field antenna for use by the above-outlined common non-contact
power transmission system. Basically, this near-field antenna has the
same shape and the same structure on both the transmission side and the
reception side, and constitutes a coil for generating a magnetic field.
That is, a transmission-side coil or an inductor 27 is formed spirally
over the surface of a substrate 26.

[0037] FIG. 13 accompanying this description shows a typical electrical
circuit of a non-contact power transmission system that uses the
above-outlined near-field antennas. In FIG. 13, the transmission side
includes a high-frequency source (Source) 61 that generates a high
frequency, and a resistance (R source) 64 that represents the impedance
of the transmission circuit. Further, the near-field antenna for
transmitting power is constituted by an inductor (L1) 65, a capacitor
(C1) 63 for frequency adjustment, and an internal resistance (Rs 1) 64
stemming from the antenna wiring. On the other hand, the reception side
in FIG. 11 includes a load as a functional device and a resistance (R
load) 72 representing the impedance of the reception circuit. Moreover,
the near-field antenna for receiving power is constituted by an inductor
(L2) 75, a capacitor (C2) 73 for frequency adjustment, and an internal
resistance (Rs2) 74 stemming from the antenna wiring. The resonant
frequency of this circuit is given by the mathematical expression shown
below. In this expression, f denotes the resonant frequency; L1 stands
for the inductance of the inductor on the transmission side and L2 for
the inductance of the inductor on the reception side; and C1 stands for
the capacitance of the capacitor on the transmission side and C2 for the
capacitance of the capacitor on the reception side.

f = 1 2 π 1 L 1 , 2 C 1 , 2 [ Math
. 2 ] ##EQU00002##

[0038] The efficiency of energy transmission with a conventional resonance
system is affected by the Q-value of the resonance system. That is, a
higher Q-value increases the reactance energy accumulated in the
resonance system, and represents the characteristic of high transmission
efficiency over a narrow band. On the other hand, a lower Q-value
increases the energy consumed by the resistance as opposed to the
reactance energy, and represents the characteristic of low transmission
efficiency over a wide band. Also with the above-mentioned non-contact
power transmission system and non-contact power transmission method, the
efficiency of power transmission is affected not only by the degree of
coupling between the inductors described above but also by the Q-value of
the antennas on the transmission and reception sides. For this reason, a
non-contact power transmission system having antennas of a high Q-value
manifests the characteristic of high power transmission efficiency.

[0039] The Q-value of the antenna parts is given by the mathematical
expression shown below. In this expression f stands for frequency, L for
the inductance of the antennas, and R for the resistance of the antenna
parts.

Q = ( 2 π f ) L R [ Math . 3 ]
##EQU00003##

[0040] As can be seen from the above mathematical expression, in the
common non-contact power transmission system of which the electrical
circuit is shown in FIG. 13, the transmission and reception circuit parts
are directly connected to the antenna parts. For this reason, the
impedance of the transmission and reception circuits appears as the
resistance in the above mathematical expression, which contributes to
lowering the Q-value of the antennas. Consequently, the system turns out
to be a resonance system with a poor resonance characteristic and gives a
reason for lowering the efficiency of power transmission. Thus the
inventors of this invention concluded that the lowered Q-value mentioned
above constitutes a cause for limiting the distance of power
transmission.

[0041] The present invention has been made in view of the above-described
results of the inventors' examination. This invention has thus been
brought about on the findings that even if the distance between the
inductors is extended and the degree of coupling therebetween is lowered
accordingly, the overall efficiency of power transmission of a
non-contact power transmission system can be improved as long as an
elevated Q-value of the antennas is maintained.

<Principles of Non-Contact Power Transmission of the Present
Invention>

[0042] The non-contact power transmission system thus implemented
according to this invention has a first inductor for resonance and a
second inductor coupled with the first inductor as the near-field
antennas for transmission and reception, the inductors being formed over
the same substrate. Further, the first inductor is connected with a
capacitor for frequency adjustment in order to achieve resonant frequency
synchronization. The second inductor exchanges power with the first
inductor through electromagnetic inductance generated therebetween, and
the second inductor is directly connected with the transmission circuit
or reception circuit. That is, the first inductor is isolated
galvanically from the above-mentioned transmission circuit or reception
circuit.

[0043] The near-field antenna of the present invention, configured using
the first inductor for resonance and the second inductor for coupling, is
thus isolated galvanically from the transmission circuit and reception
circuit, compared with the near-field antenna of the above-mentioned
common non-contact power transmission system. For this reason, the
impedance of the transmission and reception circuits does not directly
affect the Q of the inventive antenna. The Q of the near-field antenna
can thus be kept high. Consequently, a high level of transmission
efficiency is brought about between the transmitting antenna and the
receiving antenna.

[0044] In addition, the inventive near-field antenna configured using the
first inductor for resonance and the second inductor for coupling is
formed on the sample plane across which the vertical distance between the
inductors is zero (0). This makes it possible to raise the degree of
electromagnetic induction coupling between the two inductors and to
implement high transmission efficiency therebetween.

[0045] And the efficiency of transmission with the near-field antenna of
the present invention is expressed as the product of the efficiency of
transmission between the first inductor for resonance and the second
inductor for coupling on the transmission side, of the efficiency of
transmission between the first inductor for resonance and the second
inductor for coupling on the reception side, and of the efficiency of
transmission between the resonance coils of the near-field antenna on the
reception side.

[0046] Thus in the configuration of the near-field antenna of the present
invention, the antenna for the common non-contact power transmission
system is separated galvanically between the inductor for resonance and
the inductor for coupling so as to maintain a high Q of the near-field
antenna. As a result, even if the distance between the two antennas is
extended and the degree of coupling between the inductors for resonance
of the transmitting and receiving antennas is lowered accordingly, it is
possible to bring about higher efficiency of power transmission than with
the common non-contact power transmission system. Consequently the
distance of transmission can be extended.

Example 1

[0047]FIG. 2 accompanying this description shows a theoretical
configuration of a near-field antenna for non-contact power transmission
as example 1 of the present invention. In FIG. 2, a first inductor 31 for
resonance and a second inductor 33 coupled with the first inductor are
formed over the same substrate 30. Between both ends of the first
inductor 31, a capacitor 32 for frequency adjustment is connected
interposingly. And the transmission circuit or reception circuit is
connected to both ends of the second inductor. In the configuration of
the example 1, the first inductor 31 is positioned inside the second
inductor 33 over the same substrate 30. The two inductors exchange energy
therebetween through a high degree of electromagnetic induction coupling.

[0048]FIG. 3 accompanying this description is a perspective view of the
above-described near-field antenna for non-contact power transmission as
the example 1. The first inductor 31 and second inductor 33, both made of
thin metallic films, are formed over the substrate 30 composed of a
dielectric material. The material of the dielectric substrate can be made
of FR-4, a ceramic substrate, a glass substrate, or a high-resistance
silicon, for example.

[0049] As can be seen from FIG. 3, the first inductor 31 and the second
inductor 33 are formed over the surface of the dielectric substrate 30.
Also, the first inductor 31 is formed along the outer periphery of the
substrate 30 and the second inductor 33 is formed inside the first
inductor 31. Further, at the approximate center of the substrate 30, a
pair of electrode plates 32u and 32d positioned with the
dielectric substrate 30 interposed therebetween (i.e., on both sides of
the substrate) make up a capacitor 32. The capacitor 32 is connected to
both ends of the first inductor 31 as explained above, by way of
conductors formed on both sides of and through the substrate. The
capacitor 32 is provided for resonant frequency synchronization. In the
example of FIG. 3, the capacitor is constituted as a so-called parallel
plate type capacitor using electrodes formed on both sides of the
dielectric substrate in a manner opposite to each other across the
substrate. However, the capacitor is not limited to the illustrated
example; it may alternatively be a chip capacitor that can be mounted on
the surface of the dielectric substrate 30, or a variable capacitor
having the capability of frequency modulation. In particular, the example
1 configured to have the capacitor 32 positioned inside the first
inductor 31 at the approximate center of the substrate 30 makes it
possible to constitute the entire near-field antenna in smaller
dimensions than before.

[0050]FIG. 4 shows an electrical circuit of a non-contact power
transmission device utilizing the above-described example 1 of this
invention. As can be seen from FIG. 4, on the transmission side, the
first inductor 31 (L1) constituting the near-field antenna is isolated
galvanically from the transmission circuit. The transmission circuit
includes an AC power source 14 that generates a high frequency, and has
the impedance (R source) 62 of a transmission circuit that contains the
AC power source 14 and the inductance (L source) of the coupling inductor
33. The high frequency from the AC power source is transmitted from the
second inductor 33 (L source) to the first inductor 31 (L1) through
electromagnetic induction. The near-field antenna for transmitting power
is constituted by the first inductor 31 (L1) as the resonance inductor,
by the capacitor (C1) 32 for frequency adjustment, and by an internal
resistance (Rs 1) 64 stemming from the near-field antenna wiring.

[0051] Also on the reception side, the first inductor 31 (L1) constituting
the near-field antenna is isolated galvanically from the reception
circuit. The reception circuit includes the load 24 as a functional
device indicated as an impedance (R load), and an inductance (L load) of
the coupling inductance 33. And the reception-side near-field antenna for
receiving power from the transmission side is constituted as explained
above by the first inductor 31 (L2) as the resonance inductor, by a
capacitor (C2) for frequency adjustment, and by an internal resistance
(Rs 2) stemming from the near-field antenna wiring.

[0052] Thus the non-contact power transmission device of the present
invention in particular has its near-field antenna isolated galvanically
from the transmission circuit or from the reception circuit unlike the
common non-contact power transmission device. This makes it possible to
maintain a high Q-value of the near-field antenna. And as illustrated,
the non-contact power transmission device of this invention carries out
power transmission in three stages, to be explained below.

[0053] First of all (1), on the transmission side, power transmission
takes place between the coupling inductor 33 with a high degree of
coupling and the resonance inductor 31. Next (2), power transmission is
carried out through near-field magnetic field coupling between the first
inductor 31 (L1) as the transmission-side antenna and the first inductor
31 (L2) as the reception-side antenna, both antennas having a high Q
each. And finally (3), on the reception side, power transmission is
brought about between the resonance inductor 31 and the coupling inductor
33 having a high degree of coupling therebetween. For this reason, the
efficiency of power transmission with the non-contact power transmission
device of this invention is represented by the product of the levels of
transmission efficiency in the above-described three stages. In each
stage, power transmission is carried out under conditions of high
transmission efficiency, so that the inventive non-contact power
transmission device provides higher efficiency of power transmission than
the prior-art non-contact power transmission device having a low Q. In
other words, it is possible to maintain a high Q even if the distance
between the antennas is extended and the degree of coupling therebetween
is lowered accordingly.

Example 2

[0054] Next, FIG. 5 shows a theoretical configuration of a near-field
antenna for non-contact power transmission as example 2 of the present
invention. In the example 2, as in the example 1, the first inductor 31
for resonance and the second inductor 33 coupled with the first inductor
are formed over the same substrate 30 made of a dielectric material.
However, unlike the example 1, the example 2 has the first inductor 31
positioned outside the second inductor 33 over the same substrate 30. The
two inductors exchange energy therebetween through a high degree of
electromagnetic induction coupling. Also in the example 2, the capacitor
32 for frequency adjustment is connected to the first inductor 31, and
the above-mentioned transmission circuit or reception circuit is
connected to the second inductor 33.

[0055] FIG. 6 is a perspective view of the near-field antenna for
non-contact power transmission as the above-described example 2. The
first inductor and the second inductor, both made of a metallic material,
are formed over the dielectric substrate. Also in the example 2, the
material of the dielectric substrate 30 can be made of FR-4, a ceramic
substrate, a glass substrate, or a high-resistance silicon, for example.
And as can be seen from FIG. 6, the first inductor 31 and the second
inductor 33 are formed over the surface of the dielectric substrate 30,
and the first inductor 31 is positioned inside the second inductor 33.
The above-mentioned capacitor 32 for resonant frequency synchronization
is attached to the first inductor 31. In the example 2, at an edge of the
dielectric substrate 30, the capacitor 32 is formed by a pair of
electrode plates 32U and 32D with the dielectric substrate 30
interposed therebetween (i.e., on both sides of the substrate). The
capacitor 32 is connected to both ends of the first inductor 31 as
explained above, by way of conductors formed on both sides of and through
the substrate. The capacitor is not limited to the illustrated example;
it may alternatively be a chip capacitor that can be mounted over the
surface of the dielectric substrate 30, or a variable capacitor having
the capability of frequency modulation.

[0056] The near-field antenna of the above-described configuration for
non-contact power transmission as the example 2 of this invention has the
same workings and offers the same effects as the example 1 discussed
above. And the non-contact power transmission device of the example 2
also provides power transmission in three stages as discussed above. The
efficiency of transmission with this non-contact power transmission
device is also represented by the product of the levels of transmission
efficiency in the three stages. This makes it possible for the inventive
non-contact power transmission device to bring about a higher level of
power transmission efficiency than the prior-art non-contact power
transmission device having a low Q. That is, even if the distance between
the antennas is extended and the degree of coupling therebetween is
lowered accordingly, it is possible to maintain a high Q.

Example 3

[0057] Next, FIG. 7 accompanying this description shows a theoretical
configuration of a near-field antenna for non-contact power transmission
as example 3 of the present invention. That is, in the example 3, the
first inductor 31 for resonance is formed over the same dielectric
substrate 30, with both ends of the inductor 31 connected to the
capacitor 32 for frequency adjustment. Unlike the above-described example
1 or 2, the example 3 has a second capacitor 34 positioned adjacent to
the (first) capacitor 32 for frequency adjustment without the second
inductor being formed over the same substrate 30. The second capacitor 34
is connected to the transmission circuit or reception circuit.

[0058]FIG. 8 accompanying this description is a perspective view of the
above-described near-field antenna for non-contact power transmission. As
can be seen from this perspective view, the first capacitor 32 and the
second capacitor 34 are positioned in close proximity to each other along
with the first inductor 31 made of a metallic material over the
dielectric substrate 30. More specifically, the capacitors 33 and 34 are
formed by a pair of electrode plates 32u and 32d by a pair of
electrode plates 34u and 34d, respectively, on both sides of
the dielectric substrate 30 whose material is typically FR-4, a ceramic
substrate, a glass substrate or a high-resistance silicon, the capacitors
32 and 34 being positioned in close proximity to each other. The first
capacitor 32 and the second capacitor 34 are each constituted as a
so-called parallel plate type capacitor using electrodes formed with the
dielectric substrate 30 interposed therebetween.

[0059] And the electrode plates 32u and 32d and the electrode
plates 34u and 34d are positioned on both sides of the
dielectric substrate 30 in close proximity to one another with the
substrate 30 interposed therebetween. For this reason, the first
capacitor 32 and the second capacitor 34 are coupled capacitively. That
is, in the case of the near-field antenna of the example 3 of this
invention, the first capacitor 32 and the second capacitor 34 exchange
energy through a high degree of capacitive coupling therebetween. In the
example 3, as shown in FIG. 8, the electrode plate 32d of the first
capacitor 32 and the electrode plate 34d of the second capacitor 34
on the bottom (back) side of the dielectric substrate 30 are formed as
comb-tooth electrodes of which the concave and convex portions are
opposed in a manner alternately engaged with one another, whereby a high
degree of capacitive coupling is ensured between the first capacitor 32
and the second capacitor 34. In addition to the above-described use of
comb-tooth electrodes, there are many other ways available to establish
capacitive coupling between the first capacitor and the second capacitor,
and any one of them may be adopted.

[0060]FIG. 9 accompanying this description shows an electrical circuit of
a non-contact power transmission device utilizing the near-field antenna
as the above-described example 3 of this invention. As can be seen from
FIG. 9, on the transmission side, the first inductor 31 (L1) constituting
the near-field antenna is isolated galvanically from the transmission
circuit that includes the AC power source 14. However, the high frequency
from the AC power source 14 is transmitted to the first inductor 31 (L1)
through the above-described high degree of capacitive coupling between
the first capacitor 32 and the second capacitor 34. In FIG. 9, the
impedance (R source) of the transmission circuit on the transmission side
is indicated by reference numeral 62, and the second capacitor 34 serving
as the coupling capacitor is represented by a capacitance (C_source). And
the near-field antenna for transmitting power is constituted by a
resonance inductor (L1), by a capacitor (C1) for frequency adjustment,
and by an internal resistance (Rs 1) stemming from the near-field antenna
wiring.

[0061] On the reception side, in like manner as described above, the
reception circuit is isolated galvanically from the near-field antenna.
In the reception circuit, the load 24 including a functional device is
represented by an impedance (R load). The coupling capacitor (second
capacitor) 34 in the reception circuit possesses a capacitance (C_load).
And the near-field antenna (first antenna) 31 for receiving power from
the above-mentioned transmission side is constituted by the inductance
(L2) of the resonance inductor, by the capacitance (C2) of the capacitor
for frequency adjustment, and by an internal resistance (Rs 2) stemming
from the near-field antenna wiring.

[0062] Thus compared with the common non-contact power transmission
device, the non-contact power transmission device using the near-field
antenna of the example 3 has the transmission circuit or the reception
circuit isolated galvanically from the near-field antenna through
capacitive coupling, making it possible to maintain a high Q-value of the
transmitting and receiving antennas. This allows the non-contact power
transmission device of the present invention to bring about higher
transmission efficiency than the prior-art non-contact power transmission
system having a low Q-value. That is, even if the distance between the
antennas is extended and the degree of coupling therebetween is lowered
accordingly, a high Q can be maintained.

[0063] As is clear from the configurations shown in FIGS. 7 and 8, the
near-field antenna of the above-described example 3 of this invention
need only have the first inductor 31 formed over the dielectric substrate
30 as a spiral-shaped coil. For this reason, the example 3 is easier to
manufacture than the above-described examples 1 and 2. It is also
possible to make the entire device (substrate) of the example 3 smaller
in shape than the other examples.

[0064] Furthermore, the graphic representation of FIG. 10 accompanying
this description shows a comparison in power transmission efficiency
between the non-contact power transmission system of this invention and
the prior-art non-contact power transmission device. The size of the
coils used on non-contact IC cards such as SUICA offered by East Japan
Railway Company was applied to calculating the levels of transmission
efficiency. Also, the coil size was assumed to be the same as that of the
inductor (inductor size: 70×40 mm 2; inductor width: 1 mm;
inductor turn count: 1; inductor material: lossless metal), and the
distance between the inductors with regard to the inductor size was
defined as the normalized distance varied from "0" to "3" in calculating
the levels of transmission efficiency.

[0065] Under the above-described conditions, the inductance of the
inductors was 0.14 μH. Where a 10-pF capacitor was connected in
series, the resonant frequency was 42 MHz. When the internal resistance
of the near-field antenna was brought to 1Ω, the Q-value of the
prior-art non-contact power transmission device was 2.5 while the Q-value
of the non-contact power transmission device of this invention was 37.3.
That is, the Q-value was improved about 15-fold.

[0066] Also, when the practical level of the efficiency of non-contact
power transmission was set to 0.5, for example, the normalized distance
with the prior-art non-contact power transmission device remained at
about 0.1 while the normalized distance with the non-contact power
transmission device of this invention could be extended to about 0.9.
These findings confirmed that the inventive device is capable of
significantly improving the efficiency of transmission.

[0067] Lastly, FIG. 11 accompanying this description shows changes in the
ratio of power transmission efficiency between the inventive non-contact
power transmission device and the prior-art non-contact power
transmission device (=efficiency of the inventive system/efficiency of
the prior-art system). That is, as can be seen from the curve in the
figure, where the normalized distance is "0" on the horizontal axis, the
ratio of transmission efficiency between both devices is about "1"
(approximately equal). However, as the distance is extended, the ratio of
transmission efficiency is improved significantly. When the normalized
distance is later brought to "1.5" or longer, the ratio is confirmed to
be stable at about "220." This result means that if the antenna of the
non-contact power transmission device according to this invention is
adopted, the efficiency of transmission is improved 220-fold compared
with the prior-art non-contact power transmission device. That is, even
if the distance between the antennas is extended and the degree of
coupling therebetween is lowered accordingly, it is possible to maintain
a high Q.